Methods for grinding (“edging”, in the jargon) the borders of glass panes as they result after they have been cut into the final formats for use are currently known. In principle, the grinding operation can be applied to any step of the working of the glass pane, for example before toughening.
Edging is performed for two reasons: the first reason relates to safety in handling said panes, the edges of which would be dangerously sharp if they were not ground. The second reason relates to eliminating the border defects of panes, typically so-called microcracks, which may trigger breakage of the pane in subsequent working steps (particularly during toughening) as well as in subsequent use.
In order to better understand the configuration of the glass pane, not so much in its possible separate use but especially in its use in combination with other components in order to constitute a so-called double-glazing unit, some concepts related to the intermediate component, i.e. the glass pane, and the final product, i.e. the double-glazing unit, are summarized hereafter. The subsequent use of the double-glazing unit, i.e. as a component of doors and windows, is known to the person skilled in the art and is not discussed here in detail.
With reference to FIG. 1, the double-glazing unit is typically constituted by two or more glass panes 1001, 1002, which are mutually separated by one or more spacer frames 1003, which are internally hollow and are provided with microperforations on the side directed toward the inside of the unit.
The spacer frames 1003 usually contain, in their hollow part, hygroscopic material, which is not shown in the figure. The chamber (or chambers) 1006 delimited by the glass panes 1001 and 1002 and by the frame 1003 may contain air or gas or mixtures of gases injected therein, which give the double-glazing unit particular properties, for example thermal insulation and/or soundproofing properties. The glass panes and the frame are mutually joined by means of two levels of seal: the first seal 1004 is adapted to provide a hermetic closure and affects the lateral surfaces of the frame 1003 and the portion adjacent thereto of the glass panes 1001, 1002; the second seal 1005 affects the compartment constituted by the outer surface of the frame and by the faces of the glass panes up to their borders and is adapted to provide cohesion between the components and to maintain the mechanical strength of the coupling between them.
FIG. 1 illustrates five possible sectional views of configurations of the double-glazing unit 1A, 1B, 1C, 1D, 1E, only the first of which has been described. However, it is straightforward to extend the considerations made above to the configurations 1B–1E, in which a plurality of frames or of panes are provided, said panes being optionally laminated. In the figure, the sun schematically represents the outside environment of a building in which the double-glazing units are installed, and the inside of the building is represented schematically by a radiator.
The glass panes used in the composition of the double-glazing unit may have different configurations depending on their use: for example, the outer pane 1001 (with respect to the building) may be normal or reflective in order to limit the input of heat during summer months, or can be laminated/armored (1D) for intrusion/vandalism prevention functions, or can be laminated/toughened (for security functions) or combined, for example reflective and laminated.
The internal pane 1002 (with respect to the building) may be normal or of the low-emissivity type, in order to limit heat loss during winter months, or laminated/toughened (for security functions) or combined (1E), for example of the low-emissivity type and laminated.
The brief summary provided above already makes it evident that a production line, in order to obtain the double-glazing unit, requires many operations in sequence and that both the intermediate components (i.e. the glass panes) and the finished product (i.e. the double-glazing unit) have the edges of the glass panes that are accessible for contact with the hands of the operators and users. It is therefore important to increase safety by beveling the peripheral borders of the glass panes. If the finished product, which in any case has a considerable added value with respect to the individual pane, had sharp pane borders or sharp-edged panes, it would be degraded in terms of quality and commercial value.
The processes for producing the double-glazing unit are typically numerous, and each one requires a corresponding particular machine to be arranged in series with respect to the other complementary ones. Some processes or operations, cited by way of non-limiting example and at the same time not all necessary, are the following:    REMOVAL, on the peripheral face of the pane, of any coatings in order to allow and maintain over time the bonding of the sealants;    WASHING of the individual panes, alternating an inner pane with an outer pane (the orientation being the one defined above);    APPLICATION OF THE SPACER FRAME: the previously manufactured frame, filled with hygroscopic material and coated on its lateral faces with an adhesive sealant, which has a sealing function, is applied to one of the panes that constitute the double-glazing unit in a specifically provided station of the double-glazing unit production line;    COUPLING AND PRESSING of the assembly constituted by the panes and the frame or frames;    FILLING WITH GAS of the chamber or chambers thus obtained;    SECOND SEALING.
The processes listed above may be performed by the respective machine automatically or semiautomatically, but in any case entail contact of the intermediate components and of the finished products with the operator, for example during loading and unloading of the line and in subsequent steps for storage, transport, assembly and installation of the double-glazing units.
In known manual processes, the glass panes, rested on supporting surfaces, are placed in contact with belt grinders, which are arranged sequentially and are angularly staggered so as to bevel both edges of the side of the pane (methods of this type are disclosed for example in DE-A 44 19 963). The main drawbacks that arise from the known methods described above relate to the considerable bulk and cost of the machines, to the complex operations for process maintenance (such as replacement of the abrasive belts), the less than optimum quality of the grinding operation, the abnormal behavior of the belt in interaction with the pane when its width does not overlap the pane completely (i.e. at the end of the side of the pane), and finally the excessively long production times.
EP-A 0 920 954 discloses an apparatus for beveling panes of cut glass that uses two belt grinders.